Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same, which are suitable, for instance, for a broadcasting television camera, a video camera, a digital still camera, a silver-halide film camera and the like.
Description of the Related Art
In recent years, an image pickup apparatus such as a television camera, a silver halide film camera, a digital camera and a video camera has been desired to be provided with a zoom lens which has a large aperture ratio, a high zooming ratio, and a high optical performance besides. As for the zoom lens having the large aperture ratio and the high zooming ratio, a positive-lead type of four-unit zoom lens is known which has a lens unit having a positive refractive power arranged in the side closest to the object side and includes four lens units as a whole. As for this four-unit zoom lens, a zoom lens is known which has the following lens units in order from an object side to an image side: a first lens unit for focusing; a second lens unit for zooming, which has a negative refractive power; a third lens unit for correcting the variation of an image plane incident to zooming, which has a positive or negative refractive power; and a fourth lens unit for imaging, which has a positive refractive power.
In this type of four-unit zoom lens, a zoom lens is known which specifies an Abbe constant of a material of a part of the lens in the fourth lens unit, and thereby adequately corrects chromatic aberration, in particular, lateral chromatic aberration, and obtains a high optical performance (U.S. Pat. No. 7,885,014). In addition, in this four-unit zoom lens, a zoom lens is known which employs an optical material having anomalous dispersibility, adequately corrects chromatic aberration, and has a high optical performance and a high zooming ratio (U.S. Pat. No. 5,831,771 and U.S. Pat. No. 6,825,980).
The previously described positive-lead type of the four-unit zoom lens comparatively easily achieves the high zooming ratio. However, when the zoom lens acquires the high zooming ratio, the variation of the various aberrations increases, and it becomes difficult to obtain the high optical performance in an entire zoom range. In particular, chromatic aberration such as the lateral chromatic aberration and axial chromatic aberration occurs in many cases.
In order that the positive-lead type of the four-unit zoom lens adequately corrects the chromatic aberration and obtains the high optical performance while acquiring the high zooming ratio, it is important, for instance, to appropriately set the configuration of the fourth lens unit for imaging. If the configuration of the fourth lens unit is not appropriately set, it becomes difficult to correct the lateral chromatic aberration and the axial chromatic aberration, and to obtain the high zooming ratio and the high optical performance in an entire zoom range.
An object of the present invention is to provide a zoom lens which has a high zooming ratio, adequately corrects chromatic aberration in an entire zoom range from a wide angle end to a telephoto end, and has a high optical performance in the entire zoom range, and to provide an image pickup apparatus having the same.